These monitoring tools have been developed to help farmers and advisers in Southern Australia think about the sustainable carrying capacity of paddocks. They are based on results obtained during the Grassland's Productivity Program (GPP). In addition to the GPP results, we have added the additional requirement that groundcover should not fall below critical levels. Below these thresholds indicate that paddocks are being pushed too hard and stocking rates should be reduced to meet minimum groundcover requirements.
These tools are suitable for use in winter dominant rainfall areas of southern Australia growing improved pasture species (sub. clover, phalaris, perennial ryegrass, cocksfoot etc) with common annuals (annual ryegrass barley grass, silver grass etc). Potential carrying capacity in summer rainfall areas and on native grass dominant pastures seems to be much lower than for temperate improved species in southern Australia.
The tools allow farmers to calculate the potential carrying capacity – this is not a recommendation to run your paddocks or farm at this level, but set a benchmark of what is possible. If stocking rates are well below the benchmark, then it is a prompt to ask other questions such as whether there are soil fertility or subsoil constraints that are limiting carrying capacity.
The potential carrying capacity is for moderately fertilised pastures, sown to perennial grasses and annual clovers with volunteer annual grasses. Whilst annual pastures may also carry similar amounts of stock in some years, there is much higher risk of groundcover not being able to be maintained in dry years. The tools are not suitable for native pastures on low fertility soils.
As part of monitoring for Environmental Management Systems (EMS), we felt that a monitoring tool was needed as an addition to both Prograze and the 'Tips and Tools' produced from the Sustainable Grazing Systems Key Program. The monitoring tools can be used by themselves, or as part of justifying and improving on-farm environmental performance using an EMS.
Definitions and background to the potential carrying capacity calculations
What is a DSE?
DSE stands for 'dry sheep equivalent' and is a standard unit used to compare the feed requirements of classes of livestock and to assess the carrying capacity of a farm or paddock. The standard DSE is the amount of feed required by a 2 year old 45 kg Merino sheep (wether or nonlactating, non-pregnant ewe) to maintain its weight. Expressed in metabolisable energy or mega- joules/day) one DSE is equivalent to 7.6 MJ/day. DSE ratings for stock types are shown in Table 1 and more detailed information can be found in papers at the end of this document.
What is potential carrying capacity? The potential carrying capacity of a paddock or farm is the number of stock expressed as DSE per hectare that can be carried through most years. In a drought, it will not be possible to maintain the potential carrying capacity, as pasture growth is often less than half of the usual production.
The potential carrying capacity is the stocking rate that other farmers across southern Australia have achieved on paddocks on their farms under commercial conditions. The results are relevant to farmer paddocks and cover a wide range of soils, rainfalls, pastures and livestock enterprises. Because the potential is related to the length of the growing season, it means like farms are compared.
The potential carrying capacities used in this document are taken from results from the Grassland's Productivity Program that ran across southern Australia between 1994-97. The program compared two paddocks on each farm, a control paddock where the farmer continued normal farm practice and a Productivity paddock where improved fertiliser, grazing and pasture management was implemented with the assistance of experienced advisory staff. The potential carrying capacity was calculated from these latter Productivity paddocks. As such, they were not the "best" paddocks available as many farmers took advantage of GPP to upgrade poor performing paddocks. However, the results provide a good comparison of what over 100 farmers across SA, Vic, NSW and Tas were able to run on paddocks over 2 years.
Running farms close to the potential carrying capacity is important, as many studies, such as the south-west Victoria Monitor Farm Program, have consistently shown that farms, which spend more on inputs and run higher stocking rates, are more profitable than farms with lower stocking rates. However, overgrazing will degrade the farm in the longer term. This tool is designed to help balance these two goals.
What is groundcover?
Groundcover is the amount of plant material (dead or alive) which covers the soil surface. It is usually expressed in percentage terms – 100% groundcover means that the soil cannot be seen and 0% groundcover is bare soil. Groundcover can be estimated visually and the attached photos (Figure 1, Figure 2 and Figure 3) provide some examples. Work in eastern Australia has shown that soil erosion is markedly increased where the groundcover drops below 70%. In Western Australia and the Mallee regions, commonly 50% groundcover is used as the minimum threshold. Where pasture species break down rapidly when they die off (eg sub. clover and capeweed) it can be difficult to maintain 70% groundcover, this can lead to wind or water erosion.
Monitoring Potential Carrying Capacity
Goal: To stock farms or paddocks to balance the long term productivity (profitability) and environmental sustainability.
Step 1: Calculate the area of the paddock (or farm)
Note that if you have fenced off areas within a paddock, such as remnant vegetation, these areas should be excluded. Cropped areas need to be excluded from area calculations on a farm basis.
Step 2: Decide the time of year when groundcover is at its lowest level
A problem with highly fertile and well managed pastures is that sheep performance on dry feed can be adequate even though pastures are over grazed (eg. to less than 1000 kg/ha). The time when groundcover is at its lowest point could vary for particular paddocks on the farm and will be different for different climates. For example in cold, wet areas such as high rainfall districts in much of eastern Australia the most limiting period is in late autumn before the autumn break. For areas with hot, dry summers such as WA wheatbelt the critical time may be summer-autumn. For summer dominant rainfall environments, depending upon the paddock management, the storm activity is likely to make summer the time of highest risk.
Step 3: Estimate the groundcover at this critical time
Different levels of minimum groundcover (and herbage mass can also be important) are needed for different soil types and regions. Minimum levels for pastures in south-eastern Australia are suggested to be:
- 70% for pastures on flat and slightly sloping (<3%) land and on non-erosion prone soils (moderate-good soils generally). Herbage mass should be a minimum of 800-1200kg dry matter (DM)/ha.
- 80-90% groundcover for lighter, more erosion prone soils and where land is undulating. Minimum herbage mass should also be 1000-1500kg DM/ha.
- 90-100% groundcover for steep hill country on light and erosion prone soils (eg slopes of greater than 10%, granite or light sedimentary soils with low fertility and often high acidity). Herbage mass should be a minimum of 1500kg DM/ha.
In areas such as the Mallee and Western Australia, 50% is often used as the minimum groundcover %. If you have less than the minimum groundcover percentages at the critical time, then your stocking rate is too high for sustainability.
Groundcover % figures are given in Figures 1-6 (at the back of the document), ranging from 20-100% to help you assess your groundcover levels. (These were supplied by Greg Lodge NSW DPI for the 20, 40 and 70% levels and for the remainder, Primary Industries South Australia, 1996, Pasture Pics: easy estimation of pasture dry matter levels, Appila / Bundaleer Pasture Group, Appila, SA.)
Step 4: Calculate the current carrying capacity on the farm (or paddock)
This is the DSE/ha you normally run in this paddock. You will need to use your livestock paddock records to calculate the stocking rate for a typical year, the longer period over which you can calculate this value the better. For set-stocked conditions the calculation is straightforward. If the paddock is rotationally grazed with different types and numbers of stock, you will need to calculate the number of grazing days for each time the paddock is grazed (number of animals x dse rating x number of days). Add these grazing days for the period and then divide by the total number of days in the period. Use Tables 1 and 2 to determine DSE values for types of stock. Computer software packages can readily calculate carrying capacity of paddocks.
Step 5: Estimate the length of the growing season
The growing season is the long-term average growing season (number of months eg. 8 months for Rutherglen area, 7-10 months for Hamilton area), taken from when the opening seasonal rains normally occur and when pastures die off (for annuals) or hay off (for perennial species based pastures). Questions to consider are when you normally get an autumn break, whether the paddock dries off earlier than others because it is a lighter soil or has mostly annuals, or is on a steep slope. Estimate to the nearest half-month.
Step 6: Determine the soil P level for the particular paddock
If it is a Colwell P you will need to express in terms of its Olsen P equivalent. To approximately convert Colwell P to Olsen divide Colwell P by 1.6 for sands or sandy loam, 2.0 for loams, 3.0 for clay loams and clays. See the Soil Fertility Monitoring Tool if you would like more detailed information of soil testing and interpretation.
Step 7: Compare your current carrying capacity with the potential values
Potential Carrying capacity (DSE/ha) is shown in Table 4 depending on the Olsen P value (e.g. 10 or 20 mg P/kg), length of growing season and paddock size. Pick the closest value to your figures, don't be too fussed about absolute values. If you really want to go into detail, the equation you can use to calculate potential carrying capacity from any growing season, Olsen P or paddock sizes is shown below but for most situations, an approximation from Table 4 will be sufficient.
Carrying capacity (DSE/ha) = a + b (growing season) + c (Olsen P)
a = -8.30 for paddocks less than 20 ha in size or –11.05 for paddocks of more than 20 ha
b = growing season (expressed in months)
c = Olsen P (in mg/kg)
Step 8: How does your farm compare?
There are 4 common scenarios:
1. Farm current carrying capacity is below potential values and pasture cover exceeds minimum targets (see step 3 for these thresholds)
This will be a very common outcome from the above exercise and indicates that your carrying capacity is environmentally sustainable. If you are in this situation and want to improve your profitability, think about options to increase the number of stock on the farm (paddocks). This many require a change in the time of lambing, grazing management, fertiliser use or even animal genotype. Many other farms will also be in this situation and working together in a group and seeking advice from a local farm adviser can help can get closer to the potential carrying capacity, if you wish to increase the number of stock carried.
2. Farm current carrying capacity is above potential values and pasture cover below minimum standards (see step 3 for these thresholds)
This hopefully will be a relatively uncommon situation as farms in this category are likely to be both unprofitable and unsustainable. Farm or paddocks in this situation should be carefully evaluated to either grow more grass (extra fertiliser, re-sowing rotational grazing etc) or reduce the number of stock grazing the paddock. Immediate action is required.
3. Farm current carrying capacity is above potential and pasture cover is above minimum standards (see step 3 for these thresholds)
This is also probably an uncommon situation. Questions to be considered are; Has the current stocking rate been determined over especially favourable seasonal conditions? Is this paddock a very fertile or special in some other way? If the results are correct and a reasonable assessment of the potential, then your carrying capacity appears to be environmentally sustainable and it may still be possible to increase stocking rates but this will need to be done very carefully.
4. Farm current carrying capacity is below potential and pasture cover below minimum standards (see step 3 for these thresholds)
This may also be quite common in southern Australia. This result suggests that there are major limitations to the productive capacity of the farm (paddock) and that your farm is likely to be environmentally unsustainable. There are also likely to be improvements to be made in terms of profitability. Questions need to be asked what is restricting the growth in the paddock, soil fertility, acidity, pasture species, drainage etc. Advice from a local agronomist could help with many of these issues.
Table 1: Dry sheep equivalents (DSE) for different classes of sheep. Note that 1 DSE is equivalent to a mature Merino wether or dry ewe weighing 45 kg and maintaining its weight. DSE values for fibre goats (angora and cashmere) may be assumed to be similar to sheep at equivalent liveweight and physiological state.
|Sheep –Crossbreds||Sheep – Merinos|
|Weaned lambs||15 kg||25 kg|
|Gaining 100 g/day||0.9||1.2|
|Gaining 200 g/day||1.4||1.8|
|Mature sheep||70 kg||60 kg||40 kg||50 kg|
|Dry ewes, store wethers||1.3||1.2||0.9||1.1|
|Gaining 50 g/day||1.2||1.4|
|Gaining 100 g/day||1.5||1.7|
|Pregnant ewes, first 3 months||1.5||1.4||1.0||1.2|
|Pregnant ewes, last 2 months weeks bearing single lambs||2.4||2.2||1.4||1.6|
|Pregnant ewes, last 2 months weeks bearing twins||3.2||3.0||1.8||2.0|
|Ewes with single lamb at foot 1st 2 months lactation||2.4||3.0||2.4||3.1|
|Ewes with twin lamb at foot 1st 2 months lactation||3.6||3.3||2.8||3.3|
Table 2: Dry sheep equivalents (DSE) for different classes of beef cattle (in part from from McLaren 1997). Note that 1 DSE is equivalent to a mature Merino wether or dry ewe weighing 45 kg and maintaining its weight.
DSE at specified liveweights|
Beef cattle British breeds
|Weaned calves||200 kg||250 kg|
|Gaining 0.25 kg/day||5.5||6.5|
|Gaining 0.75 kg/day||8.0||9.0|
|Yearling||300 kg||350 kg|
|Gaining 0.25 kg/day||7||8|
|Gaining 0.75 kg/day||10||11|
|Mature cattle||400 kg||500 kg||600 kg|
|Dry cows, steers (store)||7||8||9|
|Gaining 0.25 kg/day||8||9||10|
|Gaining 0.75 kg/day||12||14||16|
|Pregnant cow, last 3 months||9||11||13|
|Cow with 0-3 month calf||14||18||22|
|Cow with 4-6 month calf||18||22||26|
|Cow with 7-10 month calf||22||25||28|
Table 3. Carrying capacity (DSE/ha) based on the length of growing season (months), Olsen P (mg/kg) and paddock size (from Saul and Kearney 2002) for annual-based and sown perennial pastures.
|Growing season (months)||5||6||7||8||9||10||11||12|
|Paddock size less than 20 ha|
|Olsen P 10 mg/kg||11||14||17||20||24||28||31||34|
|Olsen P 20 kg/kg||12||16||19||23||26||29||33||36|
|Paddock size more than 20 ha|
|Olsen P 10 mg/kg||8||11||15||18||21||25||28||32|
|Olsen P 20 kg/kg||10||13||16||20||23||27||30||33|
Pro-forma sheet for calculating the potential carrying capacity
|Step 1||Step 2||Step 3||Step 4||Step 5||Step 6||Step 7|
|Paddock name||Size (ha)||Time when feed is most limiting||Ground cover (%)||Current carrying capacity (DSE/ha)||Length growing season (months)||Olsen P value (mg/kg or ppm)||Potential carrying capacity (DSE/ha)|
French, R J (1987). Proceedings of the 4th Australian Agronomy Conference, Melbourne. pp. 140-149.
McLaren, C. (1997). Dry Sheep Equivalents for comparing different classes of livestock. search under Animals & Livestock / Sheep / Feeding & Nutrition
Saul, G.R. and Kearney, G.A. (2002). Potential carrying capacity of grazed paddocks in southern Australia. Wool Tech. Sheep Breed. 50 (3), 492-498.
Warn, L. (2003). Grazing management for productive hill country pastures: the Broadford grazing experiment (Department of Primary Industries). ISBN 1 74106 678 6
Sustainable Grazing Systems Key Program information can be found on the www.mla.com.au website. Search Tips & Tools and Fact sheets on the home page.
Primary Industries South Australia, 1996, Pasture Pics: easy estimation of pasture dry matter levels, Appila / Bundaleer Pasture Group, Appila, SA.
Photographs from: Greg Lodge, NSW DPI – 20% and 40% cover photographs. Primary Industries South Australia, 1996, Pasture Pics: easy estimation of pasture dry matter levels, Appila /
Bundaleer Pasture Group, Appila, SA - 50, 80 and 100% photographs.